screen lock/saver after timeout does not seem to work

[Andriy Gapon]

plasma 5.16.2 here.
I have Desktop Behavior -> Screen Locking -> [V] Lock screen automatically
after: 10 mins
But the screen is never locked even if I leave the system alone for more than 10
minutes.  I recall that it used to work quite recently.  Not sure when it got
broken, maybe after a plasma upgrade.

Does anyone else have this problem?
Or, on the contrary, can anyone confirm that the feature works for them?

Thank you!
-- 
Andriy Gapon